Large-scale synthesis and magnetic properties of cubic CoO nanoparticles

We present the synthesis, microstructural and magnetic characterization of cubic CoO nanoparticles with well-controlled size and shape. The as-synthesized CoO nanoparticles are stable because of the organic coating that occurred in situ. The Néel temperature is 225 and 280 K for the 42 and 74 nm CoO particles, respectively. The CoO nanoparticles exhibit anomalous magnetic properties, such as large moments, coercivities and loop shifts. These results provide evidence for the formation of spin compensated random system in CoO. The structurally distorted and magnetically disordered surface layer ferromagnetic phase played an important role in the magnetic behavior of CoO nanoparticles. The smaller is the particle size, the stronger is the contribution of the ferromagnetic phase and the more is the surface layer helpful to enhance the observed coercivity and the exchange bias.

► The CoO nanoparticles are stable because of the organic coating that occurred in situ. ► The Néel temperature is 225 and 280 K for the 42 and 74 nm CoO particles, respectively. ► The cubic CoO nanoparticles exhibit large moment, coercivity and loop shift at 5 K. ► The CoO particles contain a (structurally distorted) surface layer ferromagnetic phase. ► The anomalous behavior can be interpreted by the notion of random magnetic system.